1. Field of the Invention
This invention relates to a gas laser oscillator, and more particularly, it is concerned with improvement in stability of the laser beam to be oscillated from an orthogonal type gas laser oscillator which performs the laser oscillation by causing a laser medium gas to flow in the direction orthogonal to the resonant optical axis.
2. Description of the Prior Art
As this type of gas laser oscillator, there has so far been known, for example, a carbon dioxide (CO.sub.2) gas laser oscillator of a triaxially orthogonal discharge excitation system, in which CO.sub.2 gas molecules are used as the laser medium gas, the laser excitation is carried out by the electric discharge excitation, and the resulting laser beam is taken out in the direction orthogonal to the electric discharge direction and the flowing direction of the laser medium gas.
FIGS. 1 and 2 of the accompanying drawing illustrate a conventional orthogonal type gas laser oscillator, in which FIG. 1 is a perspective view showing a schematic construction of such gas laser oscillator, and FIG. 2 is a cross-sectional view of the orthogonal type gas laser oscillator shown in FIG. 1 taken along a line A--A. In each of these two figures of drawing, a reference numeral 1 designates an excitation range where laser excitation is carried out by electric discharge of the laser medium gas such as CO.sub.2 gas molecules, and so forth, reference numerals 2a and 2b represent electrodes oppositely disposed on both sides of the excitation range 1, a numeral 3 refers to a power source for applying an electric voltage across both electrodes 2a and 2b to form the electric discharge, and numerals 4 and 5 respectively refer to a total reflection mirror and a partial reflection mirror provided at both ends in the longitudinal direction of the electrodes 2a and 2b defining the excitation range 1. A reference letter G designates a laser gas stream of the laser medium gas flowing in the direction of arrows, and a reference letter L represents a resonant optical axis spanning between the total reflection mirror 4 and the partial reflection mirror 5.
In the following, explanations will be given as to the operations of the conventional orthogonal type gas laser oscillator in reference to FIGS. 1 and 2. First of all, a laser medium gas containing CO.sub.2 gas molecules is continuously fed into the excitation region 1, during which the flowing direction of the laser medium gas stream G is set at the right angle with respect to the resonant optical axis L. Then electric voltage is applied across the electrodes 2a and 2b from the power source 3 to form an electric discharge between them, with which the laser medium gas containing therein the CO.sub.2 gas molecules is excited and the laser beam peculiar to the CO.sub.2 gas molecules (wavelength of 10.6 .mu.m) is emitted. The thus oscillated laser beam is resonantly amplified between the total reflection mirror 4 and the partial reflection mirror 5, both of which are disposed on the resonant optical axis L, so that the laser beam output may be taken out of the partial reflection mirror 5. In this case, the resonant optical axis L of the laser beam dislocate to the drownstream side of the laser gas stream G from the center of the electrodes 2a and 2b by a quantity x, when viewed from the cross-section of the optical axis, as shown in FIG. 2. This dislocation in the resonant optical axis is derived from the particular nature of the orthogonal type gas laser oscillator such that, outside the exciting period when electrons created by the electric discharge between the electrodes 2a and 2b directly act on the CO.sub.2 gas molecules to excite them, the center of electric discharge and the center of excitation are displaced in the direction of the laser gas stream G, in the case of ordinary CO.sub.2 laser, owing to a relationship between the energy imparting time to the CO.sub.2 gas molecules of the N.sub.2 gas molecules to be mixed into the laser medium gas and the moving speed of the CO.sub.2 gas molecules. The above-mentioned quantity x is determined by various factors such as (1) a flow rate of the laser gas current G, and configuration of each of the electrodes 2a and 2b; (2) an excitation input, excitation width (l), and excitation gap (d); (3) composition and density of the laser medium gas; and others.
Since the conventional orthogonal type gas laser oscillator is constructed as such, the quantity of dislocation x between the center of electric discharge and the center of exciation varies with respect to the electric discharge input as the excitation input. On account of this, even if all the factors other than the variations in the excitation input out of the above-mentioned factors to determine the value x are fixed, the resonant optical axis L is required to be varied in correspondence to variations in the excitation input, when the laser beam output is controlled. Conversely, if it is assumed that the resonant optical axis L is fixed, there inevitably takes place an inconvenience such that the laser beam output does not vary linearly with respect to the variations in the excitation input. Further, the laser medium gas flowing into the excitation region 1 and the laser medium gas flwoing out of the excitation region 1 have a temperature difference of at every cross-section at point of the resonant optical axis L, on account of which there have been such inconveniences that the resonant optical axis L is bent or the optical distortion is created due to difference in the refractive index caused by the temperature variations of the laser medium gas. As the consequence of this, there inevitably accompany such disdvantages that the conventional gas laser oscillator lacks in stability of the optical axis of the laser beam to be generated, stability in the laser output, stabilized quality of the laser beam, and so forth, all being the important factors in the performance of the orthogonal type gas laser oscillator.
The present invention has been made with a view to improving the above-mentioned disadvantages inherent in the conventional orthogonal gas laser oscillator.